A Global Navigation Satellite System (GNSS) receiver and associated method for the reception and processing of GNSS signals. The GNSS receiver includes an antenna and an analog front-end to intercept the incoming radio-frequency signal and to convert it to an appropriate intermediate frequency for digital sampling. A baseband signal processor is organized into functionally identical channels, each dynamically assigned to a different satellite visible. The baseband signal processor processes the signal samples to generate the satellite signal channel impulse response for a number of Doppler frequency shifts. This results in a two-dimensional delay-Doppler map of satellite signal responses from which the baseband signal processor extracts the code time and carrier phase and frequency parameters as well as navigation data for timing, positioning, and environment mapping in the data processor.
Legal claims defining the scope of protection, as filed with the USPTO.
1. In a navigational system utilizing a plurality of satellites having time and orbit information, that transmit radio-frequency signals embedded with said time and orbit information, a method of obtaining a navigational solution, comprising the steps of: providing an incoming signal forward transformation system that is not satellite specific, wherein said incoming signal forward transformation system receives the radio-frequency signals from a plurality of the satellites and converts the radio-frequency signals received to a predetermined intermediate frequency, therein producing converted signals; providing a satellite specific processing system, wherein said satellite specific processing system obtains signals corresponding to different satellites contained within said plurality of satellites from said converted signals and generates a local reference code for said different satellites; obtaining a satellite signal channel transfer function; filtering said satellite signal channel transfer function to produce a filtered satellite signal channel transfer function; converting said filtered satellite signal channel transfer function to a time domain, yielding an estimated satellite signal channel impulse response, therein processing said converted signals and said reference code for each said different satellite to form a satellite signal channel impulse response estimate for each said different satellite; utilizing each said satellite signal channel impulse response estimate to extract navigation data, code time, carrier phase and frequency parameters from said radio-frequency signals; and utilizing said navigation data, said code time, said carrier phase and said frequency parameters from said plurality of satellites to produce a navigation solution.
2. The method according to claim 1 further includes the step of utilizing said satellite signal channel impulse response estimate, said navigation solution, and said navigation data to determine signal propagation and environment characteristics.
3. The method according to claim 1 , wherein said step of filtering said satellite signal channel transfer function includes the step of: zone-zeroing said satellite signal channel transfer function in those frequency bins around multiples of a code chipping rate.
4. The method according to claim 1 , wherein said step of filtering said satellite signal channel transfer function includes the step of: excising said satellite signal channel transfer function in frequency bins where noise power exceeds a pre-defined threshold.
5. The method according to claim 1 , wherein said step of obtaining said satellite signal channel transfer function includes the step of: generating a reference code spectrum from said reference code; obtaining a satellite-specific translated signal spectrum from said converted signal; and processing said reference code spectrum and said satellite-specific translated signal spectrum into said satellite signal channel transfer function.
6. The method according to claim 5 , wherein said step of obtaining said satellite-specific translated signal spectrum from said converted signal includes the steps of: holding said converted signal in a double-length time sample buffer; transforming said converted signal in double-length time sample buffer to the frequency domain to form converted signal spectrum; applying spectrum filtering to said converted signal spectrum; and processing said converted signal spectrum into said satellite-specific translated signal spectrum.
7. The method according to claim 6 , wherein said step of applying spectrum filtering to said converted signal spectrum includes the steps of: excising frequency bins of said converted signal spectrum above a pre-defined threshold.
8. The method according to claim 6 , wherein said step of applying spectrum filtering to said converted signal spectrum includes the steps of: weighting said converted signal spectrum according to a pre-defined function.
9. The method according to claim 6 , wherein said step of processing said converted signal spectrum into said satellite-specific translated signal spectrum includes the steps of: obtaining a satellite-specific signal spectrum from said converted signal spectrum by segmenting out those frequency bins that belong to the specific satellite and code of interest; and translating said satellite-specific spectrum up and down circularly along a frequency axis, thereby creating said satellite-specific translated signal spectrum.
10. The method according to claim 9 , wherein said step of translating said satellite-specific spectrum up and down circularly along the frequency axis further includes the step of looping through a range of Doppler shifts pre-selected or determined from estimated frequency.
11. The method according to claim 5 , wherein said step of processing said reference code spectrum and said satellite-specific translated signal spectrum into said satellite signal channel transfer function includes the step of: dividing said satellite-specific translated signal spectrum by said reference code spectrum at valid frequency bins.
12. The method according to claim 11 , further including the steps of: obtaining said cross-correlation spectrum by multiplying said satellite-specific translated signal spectrum and the conjugate of said reference code spectrum on a frequency bin to bin basis; and obtaining said auto-correlation spectrum by multiplying said reference code spectrum and said conjugate of said reference code spectrum on a frequency bin to bin basis.
13. The method according to claim 5 , wherein said step of processing said reference code spectrum and said satellite-specific translated signal spectrum into said satellite signal channel transfer function includes the step of: dividing cross-correlation spectrum by autocorrelation spectrum at valid frequency bins.
14. The method according to claim 1 , wherein said step of converting filtered satellite signal channel transfer function to a time domain, further includes the step of performing inverse discrete Fourier transforms for each translated signal spectrum at time lags, thereby forming a delay-Doppler map or sub-map of impulse response.
15. The method according to claim 1 , wherein said step of extracting code time and carrier phase and frequency parameters, further includes the steps of: creating a two-dimensional map of impulse response in terms of early, prompt, and late code lags vs. slower, in-sync, and faster frequency values; generating a joint code delay and carrier phase and frequency error discriminator per data window by interpolating the impulse response power over the time and frequency grid points and taking arctangent of the complex peak impulse response; processing the joint code delay and carrier phase and frequency error discriminator through a joint code and carrier tracking filter; and sending the filtered code delay and carrier phase and frequency back to said frequency to time conversion and said time to frequency conversion, respectively, therefore closing the code feedback loop and carrier feedback loop.
16. The method according to claim 1 , wherein said step of utilizing said satellite signal channel impulse response estimate to extract navigation data and code time and carrier phase and frequency parameters, further includes the steps of: detecting the presence of said signal by threshold testing; interpolating delay and Doppler estimates to a predetermined resolution; generating a pseudo range measurement from an interpolated delay estimate and a local time tag; generating a delta range measurement from the interpolated Doppler estimate and the selected Doppler shift; and generating a carrier phase measurement from an interpolated complex signal peak power and the estimated Doppler frequency.
17. The method according to claim 16 , further includes the steps of: generating an estimate of carrier to noise density ratio; achieving a navigation data bit sync based on a series of complex signal values; and formatting a time tag, pseudo range, delta range, carrier phase, carrier-to-noise ratio, and bit sync into a pre-specified set of GPS observables.
18. The method according to claim 16 , further includes the step of: decomposing an interpolated time location of the impulse response peak into an integer part and a fractional part in units of sampling interval; shifting the channel transfer function through multiplying complex exponentials by the amount of fractional part; and specifying a reduced range of delay lags around the integer part for inverse transformation of transfer function in the frequency domain to impulse response in the time domain.
19. The method according to claim 16 , further includes the step of: down-converting the received signal samples through multiplying complex exponentials by the amount of interpolated frequency location of the impulse response peak.
20. The method according to claim 16 , further includes the step of: up-converting the reference code through multiplying complex exponentials by the amount of interpolated frequency location of the impulse response peak.
21. The method according to claim 16 , further includes the step of: decomposing an interpolated frequency location of the impulse response peak into an integer part and a fractional part in units of frequency bin; and specifying a reduced range of Doppler frequency shifts for the frequency-domain Doppler removal from the converted signals or for the frequency-domain Doppler insertion for the reference code.
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July 25, 2005
December 30, 2008
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